The present invention relates to a flow switch in a fuel dispenser that is adapted to operate in high flow and low flow situations.
In a typical transaction, a consumer may drive a vehicle up to a fuel dispenser in a fueling environment. The consumer arranges for payment, either by paying at the pump, paying the cashier with cash, using a credit card or debit card, or some combination of these methods. The nozzle is inserted into the fill neck of the vehicle and fuel is dispensed into the gas tank of the vehicle. Displays on the fuel dispenser track how much fuel has been dispensed as well as a dollar value associated with the fuel that has been dispensed. The customer relies on the fuel dispenser to measure the amount of fuel dispensed accurately and charge the customer accordingly. One method customers sometimes use to control costs is to pay for a preset amount of fuel based on a dollar or volume amount. Regulatory requirements, namely Weights and Measures, require that these customers receive all of the fuel for which they have paid to a highly accurate degree.
Operating behind the scenes of this process are valves that open and close the fuel flow path and a flow meter that measures the amount of fuel dispensed. The purpose of the flow meter is to measure accurately the amount of fuel that is being delivered to the customer so that the customer may be billed accordingly and inventory tracking may be undertaken. As noted, for preset dollar or volume transactions, the consumer relies on the flow meter to measure the fuel dispensed so as to know when to terminate the fuel flow. Some meters are inferential meters, meaning that the actual displacement of the fuel is not measured. Inferential meters have some advantages over positive displacement meters. Chief among these advantages is that inferential meters typically are smaller than positive displacement meters. One example of an inferential meter that may be used is described in U.S. Pat. No. 5,689,071, entitled xe2x80x9cWIDE RANGE, HIGH ACCURACY FLOW METER.xe2x80x9d The ""071 patent describes a turbine flow meter that measures the flow rate of a fluid by determining the number of rotations of a turbine rotor located inside the flow path of the meter.
As fluid enters the inlet port of the turbine flow meter in the meter of the ""071 patent, the fluid passes across two turbine rotors, which causes the turbine rotors to rotate. The rotational velocity of the turbine rotors is sensed by pick-off coils. The pick-off coils are excited by an a-c signal that produces a magnetic field. As the turbine rotor rotates, the vanes on the turbine rotors pass through the magnetic field generated by the pick-off coils, thereby superimposing a pulse on the carrier waveform of the pick-off coils. The superimposed pulses occur at a repetition rate (pulses per second) proportional to the rotors""velocity and hence proportional to the measured rate of flow.
A problem may occur when using a turbine flow meter. When fuel flows across the rotors, the rotors acquire some rotational momentum. When the fuel flow stops, the rotational momentum causes the turbine rotors to continue to rotate, despite the absence of fuel flow. This continued movement causes the turbine flow meter to continue generating measurement signals as if fuel were still flowing. The control system that receives the measurement signals from the pick-off coils of the turbine flow meter continues to register fuel flow falsely.
A solution to the aforementioned problem must be found to use a turbine flow meter as an accurate flow meter in a fuel dispenser. The present invention provides a solution to this problem.
The fact that not all valves that open and close the fuel flow path are well suited for preset cost or preset volume transactions is also of concern when designing fuel dispensers. Typically, to assist consumers in dispensing a fuel amount corresponding to the preset amount, some fuel dispensers are equipped with a two stage valve that allows high flow conditions throughout the majority of a fueling transaction and slow flow conditions at the terminating portion of the transaction. In slow flow conditions, the rate of fuel being dispensed slows dramatically to enable the dispenser to hit the predetermined volume or desired monetary amount. The slow flow portion of a preset transaction generates a consistent flow-rate so that the two stage valve may be de-energized at the proper time to achieve the desired termination point. In this manner, the consumer may stop squeezing the nozzle handle at the appropriate time when the desired amount of fuel is dispensed. To date, the two-stage valves that achieve the slow flow and high flow conditions work reasonably well, but may not be optimized to interact with inferential flow meters. Thus, any solution that improves the use of an inferential flow meter should also address this concern.
The present invention provides a technique through which a control system in a fuel dispenser is cognizant of when fuel is flowing so that the control system may ignore extraneous signals from a flow meter. This allows the use of inferential turbine flow meters in fuel dispensers without the risk of a false reading in the amount of fuel dispensed. This technique is achieved by providing a dual piston/poppet flow switch in the fuel path within the fuel dispenser that works well in both slow flow and high flow conditions.
The dual piston/poppet flow switch acts as a valve. The valve operates in one of three modes. The first mode is the fully closed mode where both pistons are closed and no fuel flows through the valve. The valve has an optional indicator that informs the fuel dispenser control system if the valve is in this mode. The second mode is a slow flow open mode. In this mode, a secondary or bypass fuel path is open and fuel flows relatively slowly through the valve. The indicator, if present, tells the control system that the bypass fuel path is open and thus, the control system knows to accept inputs from the flow meter as non-spurious. The third mode is a high flow open mode. In this mode, a primary fuel path is open concurrently with the secondary fuel path, and fuel flows quickly through the valve. Because the secondary fuel path is open, the indicator, if present, tells the control system to accept input from the flow meter. The two fuel path arrangement helps optimize the valve for use with an inferential flow meter in slow flow and high flow situations regardless of the existence of the indicator. The indicator helps the control system of the fuel dispenser know when to accept inputs from the flow meter.
The valve has a housing with a primary fuel flow path on a primary axis of the housing. The primary fuel flow path is blocked by a normally closed primary piston. The primary piston is kept normally closed by a primary spring. A secondary fuel flow path routes around the primary piston. The secondary fuel flow path is blocked by a normally closed secondary piston. The secondary piston is likewise kept normally closed by a secondary spring. The force required to open the secondary piston is comparatively less than that required to open the primary piston. The secondary piston is also connected to a magnet or other position sensible element that acts as the indicator such that movements of the secondary piston may be detected.
In use, the valve initially receives fuel at a slow rate. This fuel hits the primary piston and is blocked. The fuel is thus shunted into the secondary fuel flow path where the fuel encounters the secondary piston. The secondary spring on the secondary piston is weak enough such that the slow rate of fuel is sufficient to compress the secondary spring, thereby opening the secondary fuel flow path. Opening the secondary piston moves the position sensible element such that a sensor may detect the movement of the position sensible element. The rate of fuel flow increases until the pressure on the primary piston is enough to compress the primary spring, thereby opening the primary fuel flow path. Fuel then flows through both the primary fuel path and the secondary fuel path during the majority of the fueling transaction.
As the fueling transaction ends, the process is reversed. The fuel flow rate slows, lowering the pressure on the primary piston. The primary spring closes the primary piston, leaving the secondary fuel path open. When the fuel flow is terminated, such as at the end of the transaction, the pressure on the secondary piston abates, and the secondary spring closes the secondary piston. The closing of the secondary piston moves the position sensible element, and the control system is informed to ignore further signals from the flow meter. Even when fuel flow is terminated abruptly and both pistons close at the same time, the movement of the position sensible element informs the control system to ignore further signals from the flow meter.
In exemplary embodiments, the indicator may be a Hall Effect sensor, an ultrasonic sensor, a magnetic reed switch, or the like, so as to help track the movement of the secondary piston.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.